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© 2020. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.

Abstract

In June 1876, June 1910, and August 2005, northern Switzerland was severely impacted by heavy precipitation and extreme floods. Although occurring in different centuries, all three events featured very similar precipitation patterns and an extratropical storm following a cyclonic, so-called Vb (five b of the van Bebber trajectories) trajectory around the Alps. Going back in time from the recent to the historical cases, we explore the potential of dynamical downscaling of a global reanalysis product from a grid size of 220 to 3 km. We investigate sensitivities of the simulated precipitation amounts to a set of differing configurations in the regional weather model. The best-performing model configuration in the evaluation, featuring a 1 d initialization period, is then applied to assess the sensitivity of simulated precipitation totals to cyclonic moisture flux along the downscaling steps. The analyses show that cyclone fields (closed pressure contours) and tracks (minimum pressure trajectories) are well defined in the reanalysis ensemble for the 2005 and 1910 cases, while deviations from the ensemble mean increase for the 1876 case. In the downscaled ensemble, the accuracy of simulated precipitation totals is closely linked to the exact trajectory and stalling position of the cyclone, with slight shifts producing erroneous precipitation, e.g., due to a break-up of the vortex if simulated too close to the Alpine topography. Simulated precipitation totals only reach the observed ones if the simulation includes continuous moisture fluxes of >200 kg m-1 s-1 from northerly directions and high contributions of (embedded) convection. Misplacement of the vortex and concurrent uncertainties in simulating convection, in particular for the 1876 case, point to limitations of downscaling from coarse input for such complex weather situations and for the more distant past. On the upside, single (contrasting) members of the historical cases are well capable of illustrating variants of Vb cyclone dynamics and features along the downscaling steps.

Details

Title
Simulations of the 2005, 1910, and 1876 Vb cyclones over the Alps – sensitivity to model physics and cyclonic moisture flux
Author
Stucki, Peter 1 ; Froidevaux, Paul 2 ; Zamuriano, Marcelo 1   VIAFID ORCID Logo  ; Isotta, Francesco Alessandro 3   VIAFID ORCID Logo  ; Messmer, Martina 4   VIAFID ORCID Logo  ; Martynov, Andrey 1   VIAFID ORCID Logo 

 Oeschger Centre for Climate Change Research, University of Bern, Bern, 3012, Switzerland; Institute of Geography, University of Bern, Bern, 3012, Switzerland 
 Institute of Geography, University of Bern, Bern, 3012, Switzerland; Federal Office for Meteorology and Climatology MeteoSwiss, Zurich-Airport, Zurich, 8058, Switzerland 
 Federal Office for Meteorology and Climatology MeteoSwiss, Zurich-Airport, Zurich, 8058, Switzerland 
 Oeschger Centre for Climate Change Research, University of Bern, Bern, 3012, Switzerland; Climate and Environmental Physics, Physics Institute, University of Bern, Bern, 3012, Switzerland; now at: School of Earth Sciences, The University of Melbourne, Melbourne, Victoria, Australia 
Pages
35-57
Publication year
2020
Publication date
2020
Publisher
Copernicus GmbH
ISSN
15618633
e-ISSN
16849981
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
2333837670
Copyright
© 2020. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.